Sothrbys aught to know in their blurb that a woman is a heroine of photography, "a woman admired for her courage, outstanding achievements, or noble qualities" not a hero
I assume that this is just a poor choice of words: "Prior to 1839, the chemistry required to fix images was known, with the German chemist Johann Heinrich Schulze discovering the sensitivity of silver salts to light in the 1720s." The problem faced by the early experimenters with photosensitive materials was that they did not know how to fix the images they were making.